1 => 1 
2 => 1 
3 => 2 
4 => 5 
5 => 15 
6 => 52 
7 => 203 
8 => 877 
9 => 4140 
10 => 21147 
11 => 115975 
12 => 678570 
13 => 4213597 
14 => 27644437 
15 => 190899322 
50 => 10726137154573358400342215518590002633917247281 

The first ten rows of Bell's triangle:
1 
1 2 
2 3 5 
5 7 10 15 
15 20 27 37 52 
52 67 87 114 151 203 
203 255 322 409 523 674 877 
877 1080 1335 1657 2066 2589 3263 4140 
4140 5017 6097 7432 9089 11155 13744 17007 21147 
21147 25287 30304 36401 43833 52922 64077 77821 94828 115975 